This invention relates generally to laser beam technology used in surgical procedures, and more particularly relates to the use of an infrared laser beam for delivery of energy to a localized area within an absorptive medium.
The use of laser beams as a tool for performing various surgical procedures, such as cutting and cauterizing various types of biological tissues, is well known in the art. The cutting action is provided by an intense local heating of the tissue due to absorption by the tissue of the laser energy in the focused laser spot. Such devices have been used previously for various surgical procedures such as dermatological port wine birthmark removal, laryngological and gynecological polyp excision and opthalmic retinal photocoagulation. One such prior art device utilizes a carbon dioxide infrared laser beam which is movably positioned by a directional mirror and focused by a lens through an intervening air interface to concentrate the laser energy and the tissue surface of a remote treatment site.
All of the prior art utilizing carbon dioxide infrared laser beam tissue treatment has been limited to the treatment of surface tissues which can be approached through an adjacent air interface. The use of this particular range of laser wave lengths for the treatment of biological tissue situated within an intervening or surrounding absorbing medium has been precluded in the prior art because the CO.sub.2 laser radiation is completely absorbed by the outer layers of fluid or tissue and the beam cannot penetrate into the underlying layers of tissue without vaporizing or damaging the outer layers. In many instances (e.g. gastric surgery, intraocular surgery, and neurosurgery) it is desirable to operate within an internal region and to localize placement of the laser energy within a highly absorptive medium without damaging the intervening and surrounding tissue. For example, if retinal vascular tissue were to be cauterized intraocularly be means of an infrared laser beam, or similarly if a bleeding gastric ulcer were to be cauterized in situ while surrounded by normal gastric fluids, these sites would lie within an absorptive medium. Previous devices utilizing this type of infrared laser beam could not be used to selectively treat tissue which was immersed within a surrounding absorptive medium, without being absorbed by the intervening tissue.